Technical Abstract:
Huanglongbing (HLB) was been reported in 2004 in São Paulo, Brazil. Assessments of diseased trees by visual symptoms were made in 36 groves from 8 farms in the Central citrus region of São Paulo State. 155 HLB spatial maps (varying from 0.1 to 34.8% of disease incidence) were analysed, considering quadrat sizes of 2x2, 4x4, 6x6 and 8x8 trees, by the binomial index of dispersion and the binary form of Taylor's power law. The binomial index of dispersion for various quadrat sizes suggested aggregation of HLB-symptomatic trees for about 40% of the plots. The relationship between log(observed variance) and log(binomial variance) was highly significant for the four quadrat sizes (R2 of 0.99, 0.97, 0.93, and 0.88 for quadrat sizes of 2X2, 4X4, 6X6 and 8X8 trees, respectively). Estimated parameters of the binary form of Taylor's power law provided an overall measure of aggregation of HLB-symptomatic trees for all quadrat sizes tested. All estimates of b and a were statistically different from 1, which indicated a general and significant pattern of aggregation of symptomatic plants for all quadrat sizes tested. Values of b were 1.03, 1.05, 1.10 and 1.09 for quadrat sizes of 2X2, 4X4, 6X6 and 8X8 trees, respectively. The degree of aggregation was positively related to disease incidence.